Implement UMA log throttling for cellular connections

chrome/browser/io_thread.cc

Index: chrome/browser/io_thread.cc
diff --git a/chrome/browser/io_thread.cc b/chrome/browser/io_thread.cc
index e6b3fabe94102f052a32ca49c6b2b8264804d969..e434dc76883f03a7e9e32654832350171f93d2cd 100644
--- a/chrome/browser/io_thread.cc
+++ b/chrome/browser/io_thread.cc
@@ -47,6 +47,7 @@
 #include "components/data_usage/core/data_use_aggregator.h"
 #include "components/data_usage/core/data_use_amortizer.h"
 #include "components/data_usage/core/data_use_annotator.h"
+#include "components/metrics/metrics_service.h"
 #include "components/net_log/chrome_net_log.h"
 #include "components/policy/core/common/policy_service.h"
 #include "components/prefs/pref_registry_simple.h"
@@ -508,6 +509,16 @@ IOThread::IOThread(
   if (value)
     value->GetAsBoolean(&is_quic_allowed_by_policy_);
 
+  // Some unit tests use IOThread but do not initialize MetricsService. In that
+  // case it is fine not to have |metrics_data_use_forwarder_|.
+  if (g_browser_process->metrics_service()) {
+    // Callback for updating data use prefs should be obtained on UI thread.
+    metrics_data_use_forwarder_ =
+        metrics::DataUseTracker::GetForwardingCallback(
+            g_browser_process->metrics_service()->GetDataUseTracker(),

[Alexei Svitkine (slow), 2016/03/31 04:32:25]

Instead of having a static GetForwardingCallback() on the DataUseTracker and
passing g_browser_process->metrics_service()->GetDataUseTracker() to it, how
about doing:

g_browser_process->metrics_service()->GetDataUseForwardingCallback(...)

Then, this call site (and the other one) only needs to depend on MetricsService
and one API function we expose, instead of two.

[gayane -on leave until 09-2017, 2016/03/31 17:54:57]

Done.

+            base::ThreadTaskRunnerHandle::Get());
+  }
+
   BrowserThread::SetDelegate(BrowserThread::IO, this);
 }
 
@@ -614,7 +625,8 @@ void IOThread::Init() {
           "466432 IOThread::InitAsync::ChromeNetworkDelegate"));
   scoped_ptr<ChromeNetworkDelegate> chrome_network_delegate(
       new ChromeNetworkDelegate(extension_event_router_forwarder(),
-                                &system_enable_referrers_));
+                                &system_enable_referrers_,
+                                metrics_data_use_forwarder_));
   // By default, data usage is considered off the record.
   chrome_network_delegate->set_data_use_aggregator(
       globals_->data_use_aggregator.get(),